The present invention relates generally to phase-to-voltage converters and, more specifically, to an alternating current driven phase-to-voltage converter.
Phase-to-voltage converters are well-known and generally include a capacitor which is charged beginning with the zero intercept of one signal and stopped at the zero intercept of the second signal such that the capacitor's voltage represents the phase difference between the two signals. Although the control signals are alternating current signals, the capacitor is charged from a source of direct current potential. Such a circuit to measure the phase difference between the current and voltage is described in U.S. Pat. No. 3,427,471 to South. A similar system to measure the difference in time between two parts of a single waveform is described in U.S. Pat. No. 3,544,813 to Bjerke. Another system using the same concept to measure the phase between a reference signal and a test signal is described in U.S. Pat. No. 2,820,432 to D'Nelly et al.
The phase-to-voltage converters of the prior art have not been designed for the monolithic environment since size and space was not a requirement. With the use of monolithic controllers, essentially for motors and other devices, there is a great need for a monolithic phase-to-voltage converter. One of the major drawbacks of the prior art system is the requirement of a direct current voltage source to charge the capacitor. Thus, there exists the need for a monolithic phase-to-voltage converter which is capable of using the alternating current voltage available in the system.